Dextrans are high molecular weight polysaccharides of D-glucopyranose units that are synthesized from sucrose by the enzyme dextransucrase. It is known that a number of bacterial species belonging to the family Lactobacilleae elaborate a dextransucrase enzyme. Ubiquitous species of such bacteria include Leuconostoc mesenteroides, Streptococcus mutans, and Streptococcus sanguis. These and similar bacteria form dextran as an extra-cellular slime. Dextran synthesizing bacteria are commonly present in the mouth, growing on the gums and teeth. The elaborated dextransucrase forms dextran from the sucrose passing through the mouth with foods or drinks, resulting in sticky deposits on the teeth.
The deposited dextran results in the formation of dental plaque, which holds aggregates of carious producing bacteria, and is known to be undesirable by contributing to caries and periodontal disease. Gibbons et al., Arch Oral Biol., 12:11 (1967); Gibbons et al., Arch Oral. Biol., 13:1249 (1968); Gibbons et al., J. Bacteriol., 98:341 (1969); and Scherp, Science, 173:1199 (1971).
It is recognized that a means for decomposing dextran or impeding its synthesis in the mouth would be of benefit in controlling plaque formation, and, ultimately, in mitigating caries and periodontal disease. See Scherp, Science, 173:1199, at 1202 (1971). In this connection, it was suggested that dextranase might be employed to decompose dextran formed in the mouth. Even if this should prove feasible, a more fundamental approach is to inhibit dextran synthesis, thereby avoiding the formation of plaque. Heretofore, however, no method has been known for inhibiting or controlling the action of dextransucrase, except to reduce or withhold sucrose from the diet. This is not easy to accomplish. It is difficult to avoid oral intake of sucrose in countries such as the United States where it is present in a wide varieties of foods and beverages. Moreover, sucrose is a natural constituent of many plant foods and, therefore, it would be expensive and impractical to completely eliminate it from normal diets.
The mechanism of action of dextransucrase has been described by Robyt et al., Arch. Biochem. Biophys., 165:634 (1974). The mechanism postulates a glucosyl and a dextranosyl covalent enzyme intermediate. The glucose is obtained from sucrose and is incorporated into the growing dextran chain by a nucleophilic displacement of the C.sub.1 of the reducing end of the dextranosyl chain by the C.sub.6 -hydroxyl of the glucosyl group forming a new .alpha.-1,6 glucosidic linkage.